The present invention relates generally to preparing a wafer for processing treatments, and more specifically, relates to configuring a wafer surface to receive active integrated circuit components via semiconductor processing treatments.
Typically, planarization of a wafer surface is performed to suitably prepare the wafer surface for treatment in which the wafer surface is used to guild integrated circuit components (e.g., a transistor). In some known techniques, planarization is conducted through chemical and mechanical action. In chemical-mechanical planarization (“CMP”) techniques, the surface of a wafer is polished using a polishing solution and a polishing plate, which is typically shaped in the form of disc. A chemical agent in the polishing solution may be capable of etching the wafer surface. Grit particles that are present in the polishing solution can be capable of eroding the surface through mechanical action. Controlled pressure using the polishing plate can also be applied to the wafer surface.
Residues that result from such CMP processes should be effectively removed because the residues can cause damage to integrated circuits, which will be subsequently formed using the wafer surface. Effective removal can also be beneficial in protecting the surface from further erosion that may exist because of the potential presence of grit particles, chemicals agent, or residues. Residues that may contribute to the continued erosion of a surface under preparation to be configured to receive active components, may include solid residues resulting from the action of the grit particles and may include metallic contaminations that possibly exist on the wafer surface. Further erosion of the surface may be undesirable because precise control over the thickness of the planarized object is sometimes required.
Residue resulting from the polishing action is dealt with in some known CMP techniques by introducing a rinsing solution in association with rotating and applying a polishing plate or another plate to the wafer surface. A plate to be used for polishing is typically selected to be “harder” (stiffer) than a plate that is to be used for rinsing.
In such CMP techniques, rinsing, which is in general conducted with a solution comprising deionized water (“DIW”), is performed in between a polishing and a cleaning step. Such techniques can often reduce the rate of production of polished wafers because the duration used for rinsing needs to be long enough to allow the polishing residues to be properly removed. This aspect is often detrimental in the industrial context.
It is known that an additive of the NH4OH/H2O2 (“SC1”) or Hl/H2O2 (“SC2”) type may be mixed with DIW to possibly increase the rate of removal of the polishing residues. One drawback of the use of such additives is that their use tends to continue the polishing action. The additive itself can chemically etch the surface of the wafer and, therefore, reduce the thickness of the wafer beyond that which was intended (e.g., by a few additional nanometers). Such further reduction may not be a problem depending on the original thickness of the wafer or depending on the level of tolerance that is available with respect to the specific thickness sought to be achieved.
Other drawbacks may additionally exist in the context of silicon-on-insulator type structures in which a thin layer of a substantially metal-free material containing silicon is subject to such CMP processes. Such structure types may include structures having a strained top layer of a host semiconductor material. Since the top layer in such structures is already thin even before polishing, the available range of tolerance the thickness of the layer can be decreased is relatively limited. Therefore, precise control over the extent of the polishing action is desired. The use of an additive (SC1 or SC2 type) while rinsing with DIW cannot be envisioned to provide the desired precision (e.g., precision in the order of plus or minus 5 nanometers).
In the context of CMP of metallic surfaces, an article by M. L. Free entitled “Using surfactants in iron-based CMP slurries to minimize residue particles” was published in the May 1998 issue of Micromagazine in which techniques for polishing a tungsten wafer with a polishing solution containing surfactants was described. Surfactant agents are typically known for example to be detergents or soaps. The Free articles is hereby incorporated herein in its entirety.
In the context of CMP processes of metal surfaces, the importance of the mechanical action of grit particles is approximately comparable to the chemical action of the etchant. This may be because large-sized grit particles (e.g., around 1 micron) that are used in the CMP process of metal surfaces such as, a tungsten surface, may not be underestimated when compared with the erosion caused by the chemical etchants. In this context, however, the grit particles may also cause damage to the surface being polished (e.g., scratches or holes) because of their considerable size. The use of surfactants in the polishing solution as shown in the M. L. Free publication can soften the abrasive action of the grit particle.
This technique, the use of a surfactant in the polishing solution, appears to have certain drawbacks when applied in the context of a wafer surface that is substantially metal free (e.g., a silicon based). In the context of the CMP of “non-metallic” wafers, the grit particles are typically smaller than the grit particles used in the CMP of metallic surfaces. As a result, the chemical action of the chemical agent in the polishing solution is typically dominant over the mechanical action of the grit particles. Since, the effect of the grit particles is less dominant in the “non-metallic” wafer context, the use of a surfactant in the polishing solution to curb the aggressiveness of the grit particles is of less concern and may disadvantageously increase production costs with little realized benefit to the end product.
Another drawback, is that the use of the surfactant will reduce productivity because it will slow the effect of the chemical agent in the polishing solution. For example, a chemical agent having a basic pH is typically used in CMP processes in planarizing silicon-based surfaces. Adding a surfactant to the CMP polishing solution for such surfaces will reduce or may even counteract the action of chemical agent in the solution because the surfactant typically has an acidic pH. This may substantially increase the wafer polishing time (e.g., increase by a factor of ten) and reduce the productivity of the fabrication line.
Therefore, improved CMP processing technologies are desired.